In a wireless communications system, coordinated multi-point transmission (Coordinated Multi-Point transmission, CoMP) is an important means of improving overall performance of a cell and performance of users at cell edges. In a CoMP system, network nodes include an evolved base station (evolved NodeB, eNB) and at least one access point (Access Point, AP). Multiple APs can coordinate to transmit and receive data of a user equipment (User Equipment, UE). The coordinating APs may be within coverage of a same base station or different base stations. For example, these APs may be different types of network nodes, including but not limited to a radio signal transceiver (Remote Radio Head, RRH), a remote radio unit (Remote Radio Unit, RRU), a relay, and a base station.
In a Long Term Evolution (Long Term Evolution, LTE) system, a physical layer demodulates corresponding time-frequency resources on a physical layer shared data channel such as a physical downlink control channel (Physical Downlink Control Channel, PDSCH) to obtain data. Because the time-frequency resources of the PDSCH channel are shared by all user equipments in a cell, when a user equipment obtains data, the network side needs to transmit, to the user equipment over a downlink control channel, information of resource blocks that transmit data for the user equipment and relevant physical layer parameters that enable the user equipment to demodulate its corresponding data correctly.
When a user is handed over between cells, the network side delivers measurement control information (Measurement Control) to the user to regulate measurement behaviors of the user and a measurement reporting criterion. The user measures neighboring cells of the access cell, and reports measurement results conforming to the reporting criterion to a network node in the form of a measurement report (Measurement Report), where the measurement report includes a cell identity conforming to the reporting criterion. The network node makes a handover decision for the user according to the measurement results reported by the user.
In measurement, the UE can use a CSI-RS to distinguish between cells covered by APs that have the same physical cell identity (Physical Cell Identity, PCI), and, through CSI-RS measurement on resources of the cells, assess signal levels and signal quality of signals received by the UE from the cells, which is also known as radio resource management (Radio Resource Management, RRM) measurement. According to the measurement result, those with optimal signal quality in an RRM measurement set are selected as a CoMP measurement set, or selected for handover. However, resource elements (Resource Element, RE) of the CSI-RS are too sparse to ensure a satisfactory measurement precision.